Marais was born in Pretoria, the thirteenth and last child of his
parents, Jan Christiaan Nielen Marais and Catharina Helena Cornelia van
Niekerk. He attended school in Pretoria, Boshof and Paarl and much of
his early education was in English, as were his earliest poems. He
matriculated at the age of sixteen. After leaving school he worked in
Pretoria as a legal clerk and then as a journalist before becoming owner
(at the age of twenty) of a newspaper called Land en Volk (lit. Land
and (the Afrikaner) People). He involved himself deeply in local
politics. He began taking opiates at an early age and graduated to
morphine (then considered to be non-habit-forming and a safer drug) very
soon thereafter. He became addicted and his addiction ruled his affairs
and actions to a greater or lesser extent throughout his life. When
asked for the reasons for taking drugs, he variously pleaded ill health,
insomnia and, later, the death of his young wife as a result of the
birth of his only child. Much later, he blamed accidental addiction
while ill with malaria in Mozambique. Some claim that his use of drugs
was experimental and influenced by the philosophy of de Quincey. He
married Aletta Beyers but she died from puerperal fever a year later,
eight days after the birth of their son, Marais' only child. In
1897—still in his mid-twenties—he went to London, initially to read
medicine. However, under pressure from his friends, he entered the Inner
Temple to study law. (He qualified as an advocate). When the Boer War
broke out in 1899, he was put on parole as an enemy alien in London.
During the latter part of the war he joined a German expedition that
sought to ship ammunition and medicines to the Boer Commandos via
Portuguese East Africa (now Mozambique). However, he was struck down in
this tropical area by malaria and before the supplies could be delivered
to the Boers, the war ended.

From 1905 he studied nature in the Waterberg ("Water mountain"), an
area of wilderness north of Pretoria and wrote in his native Afrikaans
about the animals he observed. His studies of termites led him to the
conclusion that the colony should be considered as a single organism. In
the Waterberg Marais also studied the black mamba, spitting cobra and
puff adder.He also observed a specific troop of baboons at length, from
which numerous magazine articles and the books "My Friends the Baboons"
and "The Soul of the Ape" originated. He is acknowledged as the father
of the scientific study of the behaviour of animals, known as Ethology.
As the leader of the Second Afrikaans Language Movement, Marais
preferred to write in Afrikaans and his work was translated into various
international languages either late in his life or after his death.
Southern Africa is the only place in the world where Afrikaans is spoken
to any degree, although it can be understood by Dutch and Flemish
people. His book "Die Siel van die Mier" (lit. "The soul of the ant" but
usually given in English as the "Soul of the White Ant") was
plagiarized by Nobel laureate Maurice Maeterlinck, who published "The
Life of the White Ant" in 1926, falsely claiming many of Marais'
revolutionary ideas as his own. Maeterlinck was able to do this because
he was Belgian and, though his mother tongue was French, he was fluent
in Dutch, from which Afrikaans was derived. It was common at the time
for worthy articles published in Afrikaans to be reproduced in Flemish
and Dutch magazines and journals. Marais contemplated legal action
against Maeterlinck but gave up the idea in the face of the costs and
logistics involved.

The social anthropologist Robert Ardrey said in his introduction to
The Soul of the Ape, published in 1969, that "As a scientist he was
unique, supreme in his time, yet a worker in a science unborn." He also
refers to Marais work at length in his work ' African Genesis.' Marais
was a long-term morphine addict and suffered from melancholy, insomnia,
depression and feelings of isolation. The theft of his ideas weighed
heavily on his mind and some say this caused his final demise, although
others argue that the issue had an energizing and invigorating effect.
Certainly it brought him back into the public eye in a favorable way. In
1936, deprived of morphine for some days, he finally borrowed a shotgun
(on the pretext of killing a snake) and shot himself in the chest. The
wound was not fatal and Marais therefore placed the end of the weapon in
his mouth and pulled the trigger. This occurred on the farm Pelindaba,
belonging to his friend, Gustav S. Preller. For those who are familiar
with the dark moods of certain of Marais' poems there is a black irony
here; in Zulu, Pelindaba means "the end of the business" – although the
more common interpretation is "Place of great gatherings". Marais and
his wife Lettie are buried in the Heroes' Acre, Pretoria.

Marais' work as a naturalist, although by no means trivial (he was
one of the first scientists to practice ethology and was repeatedly
acknowledged as such by Robert Ardrey and others), gained less public
attention and appreciation than his contributions as a literalist. He
discovered the Waterburg Cycad which was named after him (Encephalartos
eugene-maraisii). He is amongst the greatest of the Afrikaner poets and
remains one of the most popular, although his output was not large.
Opperman described him as the first professional Afrikaner poet; Marais
believed that craft was as important as inspiration for poetry. Along
with J.H.H. de Waal and G.S. Preller, he was a leading light in the
Second Afrikaans (language) Movement in the period immediately after the
Second Boer War, which ended in 1902. Some of his finest poems deal
with the wonders of life and nature but he also wrote about inexorable
Death. Marais was isolated in some of his beliefs, he was a
self-confessed pantheist and claimed that the only time he entered a
church was for weddings. Although an Afrikaner patriot, Marais was
sympathetic to the cultural values of the black tribal peoples of the
Transvaal; this is seen in poems such as "Die Dans van die Reën" (The
dance of the rain). The progenitors of the Marais name in the region
were Charles and Claude Marais, from the Paris region of France. The
Marais name has retained its original French spelling and pronunciation
in South Africa.

O cold is the slight wind,
and keen.
Bare and bright in dim light
is seen,
as vast as the graces of God,
the veld's starlit and fire-scarred sod.
To the high edge of the lands,
spread through the scorched sands,
new seed-grass is stirring
like beckoning hands.
O mournful the tune
of the East-wind refrain,
like the song of a girl
who loved but in vain.
One drop of dew glistens
on each grass-blade's fold
and fast does it pale
to frost in the cold!

He was educated mostly in English and his first poem "The Soldier's Grace" was written in 1883 when he was 12.

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His poem, "Die dans van die reën", was set to music by Laurinda Hofmeyr and included in her album Ligdag.
Laurika Rauch sings "Skoppensboer", set to music by Abri Helberg (a
member of the band Marimba). Marimba also set to music poems such as
"Winternag", "Mabalel" and "Diep Rivier" for the award-winning play
about Eugène's work, Uit die bloute.

·

A cycad was named after him: the Encephalartos eugene-maraisii, which he discovered in the Waterberg area.

·

In 1925 he wrote a series of articles in Die Huisgenoot about Die siel van die mier and his study of a termite's nest in the Waterberg. The Belgian Nobel Prize winner Maurice Maeterlinck, who knew Flemish and thus understood Afrikaans, included Marais' theories in his book La vie des termites, without acknowledging Marais and won international acclaim.

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Dramatist Athol Fugard wrote the script for a movie The Guest at Steenkampskraal, about a few months in Eugène's life. It was released in 1977 with Athol playing the role of Eugène.